Electrical insulation.



WILLIAM T. CUSHING, 01E MILWAUKEE, WISCONSIN, ASSIGNOR TO THE CUTLER- HAIVIIVIER MFG. COL, 0F MILWAUKEE, WISCONSIN, A CORPORATION OF WIS- Patented Feb... 5, I9T@.

CONSIN.

ELECTRICAL INSULATION.

11,255,139, Specification of Letters Patent.

No Drawing. Application filed September 9, 1915.

To all whom it may concern."

Be it known that I, WILLIAM T. CUsHING, a citizen of the United States, residing at Milwaukee, in the county of Milwaukee and State of Wisconsin, have invented new and useful Improvements in Electrical'lnsulation, of which the following is a full, clear, concise, and exact description.

This invention relates to compositions of material particularly adapted for plastic insulating compound. More specifically the invention relates to that class of materials employing an inert filler as a base and a van nish-like binder.

Varnish has proven a very effective binder 'and materials utilizing the same as such have been found very advantageous, especially for insulating purposes. However, rapid oxidation is characteristic of varnishes as a class and in the use thereof much difficulty has been experienced through premature oxidation. Premature oxidation, or other causes affecting the keeping qualities of the mixed base and binder, impair the effectiveness of the varnish as a binder through loss of its cohesive or adhesive power and sometiines render the same useless as such.

This invention has among its objects to overcome the aforesaid difficulties in the use of varnish and to provide a composition which may be kept for a considerable period of time before molding without afiecting-the final product.

A further object is to provide a composition of the aforesaid character of a rela-- tively low cost which may be advantageously used in many instances;

A still further object is to provide a sim- 'wide range.

Serial No. 49,817.

As before stated, the base comprises an inert filler and any of a number of materials may be advantageously employed therefor. Probably fibrous materials are best adapted for this purposeand in practice it is preferred to employ asbestos in view of the heat resisting properties thereof. Where asbestos is used it is preferably reduced to a comminuted state whereby when it is mixed with the binder the resultant mass will assume a granular form, particularly suited for cold molding.

The binder may employ any preferred varnish, but for purposes of economy it is preferred to form the varnish of 20 parts East India gum, 40 parts China wood oil, 3 parts rosin and sometimes 1 part lead manganese resinate. In preparing this varnish the gum is preferably melted in the China wood oil after which the rosin and lead manganese resinate are added and the mixture cooked at a temperature of 400 F. until stringy. Also, this varnish is provided with a thinning agent, hereinafter mentioned.

The retarder for the varnish preferably comprises a mixture of stearin pitch and coal tar pitch after removal from the latter of the free carbon thereof, although other materials capable of retarding oxidation may be employed. For example, vegetable oils,

such as castor oil, will prove effective retarders. When employing the aforesaid mixture the stearin pitch and coal tar p tch are preferably combined in the proportions of 2 to 1.

Inthe formation of the hinder the varnish and retarder are preferably mixed in the proportions of 3 to 1. this being accomplished in the presence of heat sufficient to melt both, a heat of 300 to 350 F. usually being sufficient. The proportion may, of course, be varied and probably through a The mixture is then cooled and thinned to working consistency by a volatile solvent as, for example, benzin. Th s completes the binder.

The base and binder may be mixed in different proportions according to the results desired and when thoroughly mixed they produce a granular mass readily susceptible of cold molding. Very satisfactory results have been obtained with a mixture of the base and binder in the proportions of 74 to 77 parts of the former and 26 to 23 of the progressed to a satisfactory point which is usually in about 24 hours. The baking temperature is lowered when other materials, such as animal or vegetable fibers are employed.

In baking, the solvent which is volatile at' the prevailing temperature is driven ofl", leaving the product extremely hard and mechan'ically strong. The product also takes.

} a good finish and is particularly adaptable for tapping.

What I claim as new and desire to secure by Letters Patent is:

1. An electric insulating composition including abase, a varnish and a mixture of stearin pitch and coal tar oxidation of the varnish.

2. An electric insulating composition including a base, ayarmsh, and an oxidation Mretarder compnsmga mixture of stearin pitch and coal tar pitch, the latter being relieved of its free carbon.

'3.' An electric insulating composition including an inert filler, a varnish and an oxidation retarder comprising a mixture of stearin pitch andcoal tar pitch the former ingredient being in excess of the latter. 4. An electric insulating composition including a base, a varnish and an oxidation retarder therefor comprisin a mixture of stearin pitch and coal tar pitch in the proportion of approximately two parts of the former to one part of the latter.

5. An electric insulating composition including an inert filler as a base, and a binder including East India gum, China wood oil and rosin mixed to constitute a varnish and further. including an oxidation retarder.

6. An electric insulating composition comprising asbestos and a binder therefor including a varnish of East India gum, China wood oil and rosin and an oxidation retarder of stearin pitch and coal tar pitch in the proportion of approximately two parts of the former to one part of the latter.

In witness whereof, I have hereunto subscribed my name in the presence of two Witnesses. pitchto retard WILLIAM T. CUSHING.

OSCAR A. KELLER. 

